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LIGO turns back on to hunt for more gravitational waves

Listening for more crashing waves

Julian Stratenschulte/DPA

By Leah Crane

LIGO is back, and it’s better than ever. On Wednesday morning, Earth’s premier gravitational wave hunter turned on for its second science run – and after the first run’s grand success, hopes are high for what this next six-month round of observation may bring.

Gravitational waves are the ripples that surge across space time when massive objects move. Although Einstein predicted their existence more than a century ago, we hadn’t seen direct evidence of them until last year. The Laser Interferometer Gravitational Wave Observatory (LIGO) saw two strong gravitational wave events in its first four months, and possibly a third weaker signal, each from a pair of black holes crashing together and merging. If that trend continues in the new run, we should see at least six events in the first half of next year – but detector upgrades may allow us to spot even more.

“If we measured 3 in the first run, we should measure something like 10 in the next half a year,” says Ilias Cholis at Johns Hopkins University in Baltimore.

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Since the end of LIGO’s first observing run in January, both of its detectors have seen significant improvements that have raised their sensitivities by up to 25 per cent for some events. A third detector in Italy, VIRGO, is expected to join the twin LIGO detectors in Louisiana and Washington state this spring. That will let us pinpoint the source of the gravitational waves and see if they emitted any light in conventional wavelengths as well.

With these higher sensitivities, researchers expect to observe more black hole mergers, which could lead to a universal map of black hole distributions. If we’re very lucky, we may also see some neutron star collisions, which can help illuminate how stars evolve and die. Eventually, we may even be able to use gravitational waves to examine the expansion of the universe.